The mining of rock and ore in mines, both above ground and below ground, takes place principally through drilling and blasting. It has become clear that the cost of mining can be considerably reduced if the technique of drilling long holes with high precision is mastered. In particular, improved possibilities to guide a drill string, and thus also a drill tool or drill bit that is situated at the front of the drill string, during drilling are aspired to, i.e., to achieve what is known as “directionally controlled drilling”. It is possible in this way to cause the drill bit to work forwards through the rock along a pre-determined pathway that may extend linearly, or may be shaped as an arc with a certain curvature. Improved possibilities for setting and guiding the direction of the drill bit during drilling can make the drilling more efficient, by making it possible to drill exclusively where it is necessary, to achieve, for example, higher efficiency through concentrating the drilling solely to those parts of the rock that contain ore. It would be desirable also to make it possible in a simple manner to set and drill, with a down-the-hole drill, based on a reference coordinate system in three-dimensions that has been established in advance, and in this way cause a drill bit not only to move along a pre-determined pathway but also to guide the drill bit such that it can reach with high precision a pre-determined goal in a three-dimensional space.
The production of a curvature or oblique placement between the drill bit and a rear part of a drill string in order to make directional guidance of a drill bit possible is previously known. In order to achieve this oblique placement, the use of various types of joint arrangement in the down-the-hole drilling equipment that can be reset into various angular conditions with the aid of control and actuator means is previously known. Energy to achieve this setting can be obtained in various ways, for example pressurised air that is supplied through a hollow drill string, or through the use of the force that arises when the drill rod rotates relative to the cavity wall. In the case of drilling with the aid of down-the-hole drilling equipment that is supplied with a working fluid through a passage that extends through the drill string, it has proved to be appropriate to use a partial flow of the said working fluid as a source of energy for the directional guidance of the drill bit.